In Situ Formation of Y sub 1 Ba sub 2 Cu sub 3 O sub x Thin Films by Physical Sputtering

We have found that in situ superconducting Y-Ba-Cu oxide thin films can be produced by sputtering without the aid of any external O sub 2 source during deposition. The films were produced by RF magnetron sputtering from a composite target onto MgO(100) substrates heated at 650C. Films made in a pure Ar pressure of 24 mTorr and fast cooled in N sub 2 ambient contain the tetragonal Y sub 1 Ba sub 2 Cu sub 3 O sub x phase with x estimated to be 6.1. Films made under the same sputtering conditions, but cooled in 30 mTorr oxygen after deposition, show a superconducting transition T sub c(R=0) at 71K with an onset at 85K. The T sub c(R=0) rises to 80K if 0.5 mTorr oxygen was added during sputtering.